Ethernious Natsu Dragneel

Zeref returns. Natsu finds a book. He opens it. All hell breaks loose.
After 2 years the guild disbanded, FairyTail returns. All the mages are happy and the future seems bright. Everything suddenly takes a turn for the worst. Will Natsu stay a demon forever or will he return to his old self? And a certain blonde mage does something no one could have foresaw.